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The last dance--who's man/woman enough for this intellectual challenge!

Discussion in 'Dental' started by rsweeney, Apr 16, 2004.

  1. rsweeney

    rsweeney Senior Member
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    All right y'all, it's pretty amazing where my cardiovascular physiology journey has taken me. One question leads to an answer and then that answer leads to another question :eek: Well, I have come to the end of the road, and it's quite a paradox. Where Dr. Guyton's contributions have been a big help in my search for the answer his ideas have now confused me---maybe :rolleyes: I, for the last time, turn to the great and brilliant minds of SDN. Following is an article from the 1962 Handbook of Physiology ~Circulation~ by Dr. Guyton when he first introduced the "Guyton analysis" or what we students commonly know as the cardiac and systemic function curves. My focus, however, is on Guyton's analysis of the relationship between increased vasomotor tone and its effect on the vascular function curve.

    THE PASSAGE:
    "Increased vasomotor tone has been caused by infusion of a sympathomimetic drug [epinephrine]. [As the rate of the sympathomimetic drug infusion was increased, the vascular function curve shifts in a parallel fashion up and to the right exactly like it does in a blood transfusion]....The slope of the venous return curve did not change, which is why it shifted in a parallel fashion. On second thought, one can understand why this is true. When vasomotor tone [arteriolar tone] is increased throughout the circulation while blood volume remains constant, pressures everywhere in the circulation will tend to rise because of tightening of the vessels around the blood. But, if any single segment of the circulation constricts, some other segment of the circulation must dilate. On average, then, for every constriction that occurs in the systemic circulation following the injection of epinephrine, there had to be equal dilation everywhere else. Indeed, measurements have shown that, as the arterioles constrict under these conditions, there is a tendency for the veins to dilate even though the walls of the veins to tighten to a very great extent. This elevates mean systemic pressure but does not increase the resistance to blood flow from the systemic veins toward the heart. In essence, then, we can say that an increase in vasomotor tone effect venous return principally by increasing the mean systemic pressure, and, usually, an increase in vasomotor tone does not increase the average resistance that opposes the return of blood to the heart."


    Issue 1)
    So do y'all see the problem. To this date ALL texts and board review series books say that an increase in vasomotor tone [which is the same thing as increased TPR] will NOT change the mean systemic pressure because the compliance and volume changes of the arterioles contribute insignificantly to the mean systemic pressure. For this reason, all texts have increased TPR shifting the vascular and cardiac function curve downward, with NO change in mean systemic pressure!

    Issue 2)
    "But, if any single segment of the circulation constricts, some other segment of the circulation must dilate. On average, then, for every constriction that occurs in the systemic circulation following the injection of epinephrine, there had to be equal dilation everywhere else...Indeed, measurements have shown that, as the arterioles constrict under these conditions, there is a tendency for the veins to dilate even though the walls of the veins tighten to a very great extent."

    ----What does that mean? All I know is that if the arterioles constrict, then TPR is up---period. The veins dilate at the same time--what? :laugh: If that was the case, then vascular function curves as we learn them are full of it. The bottom line is this. If the veins do indeed dilate as the arterioles constrict, the vascular function curve would be WAY different than what is presented to us in text books AND in the classroom. Here is a description of what the vascular function curve should look like in Guyton's scenerio, where the arterioles constrict while the veins simultaneously dilate--in my point of view:

    The vascular function curve will move downward in a parallel fashion as a result of venous dilation [or increased venous compliance]. Thus, a lower mean systemic pressure will be reached. The vascular function curve will then rotate in a counter-clockwise fashion about this new mean systemic pressure as a result of the increased TPR. That is how it should look.

    Issue 3
    So what/why is Guyton talking about folks, when he says:

    1)Arteriolar constriction causes a parallel shift upward [like in a transfusion]
    2)The veins simultaneously dilate when a segment of the arterioles constrict
    3)What does he mean when he says "if any single segment of the circulation constricts". What is "a segment"?
    4)increased vasomotor tone [increased TPR] causes a parallel shift upward on the vascular function curve----YEAH THIS IS TOTALLY WRONG
    :thumbdown:

    All I know is that only two things cause a parallel shift upward on the vascular function curve and they are as follows--according to recent texts:

    1)Increased venous tone [decreased venous compliance]
    2)Rapid transfusion of blood

    Does it have something to do with the sympathomimetic drug? Or, has Guyton been correct all these years and current physiology professors/authors have simply been misinterpreting him, thus presenting us with false information in books and in the classroom?

    Come on experts, this is the last big challenge!:idea:

    What do you think?

    Wow, this is a long one :oops:


    I love y'all :love: :luck:
     
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  3. UNLV OMS GUNNABE

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    Nothing personal but, I think you need to find a hobby or something.
     
  4. gatorfan99

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    :sleep: :sleep: :sleep: :sleep:

    I'm sorry... you lost me at "All right y'all..."



    :)
     
  5. Donotgointhere!

    Donotgointhere! Membership Revoked
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    god, what a loser....
     
  6. the big wand

    the big wand Senior Member
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    rsweeney: Are you taking a physiology course right now? Or, you're studying it just for the sake of preparing for dental school coming up?

    I wouldn't care about all those curves at all; they're pretty much useless in clinical aspect of medicine and dentistry, unless you specialize in cardiology...maybe.

    Issue 1) I thought an increase in vasomotor tone is not the same as increased resistance. A vessel that dilates can have either an increased or a decreased vasomotor tone. The same is true for a vessel that constricts. Take balloons for analogy. When you inflat/dilate the balloon to the maximal extent, the surface of the balloon (or the wall of a vessel) in fact has an increased tension/wall stress. When the balloon is deflated (or the vessel constricts), it actually goes back to its original relaxed state (= decreased tone). If you constrict the vessel even further beyond its originally relaxed state, the vessel tone increases again. Make sense?
     
  7. rsweeney

    rsweeney Senior Member
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    Thanks wand for answering my question and not just rebuking me. This is more of an obsession/passion than a hobby. I personally think this topic is very intriguing, whether or not it is clinically relevant--or even relevant at all. You have authentic teachers in this world and then you do not. And you have authentic students in this word and then you do not. And then you have those with nothing better to do than spit venom. Wand, I respect your efforts.

    As for my intentions---when I come across a question I simply cannot answer, I will NOT just pass it by and be on my way. There is nothing more frustrating than having an idea or question be deemed unconventional, and then have it riddled with riducule. Too often, people take what is taught to them as the golden rule. But what if the "rule" is just a bunch of nonsence. I think it is dangerous to accept everything we read as the rule. The only problem is that we are taught our whole lives not to challenge what's set in stone [convention], and doing so is pernicious. I take everything with a grain of salt, and I question everything--always go against the grain is where my friends and me stand. I apoligize for submitting this question/thought/thread if it's too complicated for you. SDN members are likely among the most brilliant minds in the world. If a thread like this is turned away in ridicule here, then----"Houston, we have a problem." This kind of stuff should inspire you! I will always be a blenderhead my whole life--and I will always ask so many questions--and so should you. I was with my girlfriend at a statistics seminar yesterday, and the great Professor Rao said these words, "The more knowlegable we get the more ignorant we get." And, ultimately, the more ignorant we get the more questions we ask.

    Peace y'all
     
  8. UNLV OMS GUNNABE

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    The most brilliant minds in the world? I don't think so.
     
  9. rsweeney

    rsweeney Senior Member
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    Origionally posted by gatorfan99:
    I'm sorry... you lost me at "All right y'all..."


    The most brilliant minds in the world? I don't think so.

    It's called sarcasm OMS-----you'll be ok :laugh:
     
  10. Doggie

    Doggie Professional Jackass
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    you're not making ppl do your homework are u? :laugh:
     
  11. wy2th

    wy2th New Member

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    Come on guys, this is a professional student forum and this is a professional caliber thread rsweeney posted. rsweeney does more homework than you would like to know. He has not even started school yet and he is wizzing away in phyiology, is a sub--he loves to teach--and does all kinds of random stuff. This "homework" is all voluntary, as he has not even been taught it yet. I'd say he's done pretty well. I know it's a bias statement because I am his friend, but it's true.

    Trust me, rsweeney has always been like this. He finally got me to register on SDN to type my response in. I gave him a verbal response, but I will type it in to see if SDN agrees. It's a clever find-I must admit. Since it was 1962 and Guyton was just coming up with this idea, a lot of ideas he had then were just that. His ideas then were not as refined as they are now.

    Issue 1)
    So do y'all see the problem. To this date ALL texts and board review series books say that an increase in vasomotor tone [which is the same thing as increased TPR] will NOT change the mean systemic pressure because the compliance and volume changes of the arterioles contribute insignificantly to the mean systemic pressure. For this reason, all texts have increased TPR shifting the vascular and cardiac function curve downward, with NO change in mean systemic pressure!


    I would follow what current books say. The word vasomotor refers to the arteroles. So, if the arterioles constrict, then TRP will go up as you said. Also, as you said, MSFP will not change "because the compliance and volume changes of the arterioles contribute insignificantly to the mean systemic pressure".

    Issue 2)
    "But, if any single segment of the circulation constricts, some other segment of the circulation must dilate. On average, then, for every constriction that occurs in the systemic circulation following the injection of epinephrine, there had to be equal dilation everywhere else...Indeed, measurements have shown that, as the arterioles constrict under these conditions, there is a tendency for the veins to dilate even though the walls of the veins tighten to a very great extent."

    ----What does that mean? All I know is that if the arterioles constrict, then TPR is up---period. The veins dilate at the same time--what? If that was the case, then vascular function curves as we learn them are full of it. The bottom line is this. If the veins do indeed dilate as the arterioles constrict, the vascular function curve would be WAY different than what is presented to us in text books AND in the classroom. Here is a description of what the vascular function curve should look like in Guyton's scenerio, where the arterioles constrict while the veins simultaneously dilate--in my point of view:

    The vascular function curve will move downward in a parallel fashion as a result of venous dilation [or increased venous compliance]. Thus, a lower mean systemic pressure will be reached. The vascular function curve will then rotate in a counter-clockwise fashion about this new mean systemic pressure as a result of the increased TPR. That is how it should look.


    I am not too sure what that meant when he said "if any single segment of the circulation constricts, some other segment of the circulation must dilate." Unless the drug is having some counter-effect on the veins causing them to dilate, then I don't know how else to explain it. It takes a lot for those veins to dilate. Since, however, he specifically points out that the arterioles are constricting then as we know today TPR will go up and the MSFP will not change. He was wrong. Your "point of view" of how the vascular function curve will look is right on. Actually, in exercise, the vascular function curve moves to the right in a parallel fashion due to the sympathetic venous constriction AND THEN the vascular function curve will shift in a counter-clockwise fachion about that new MSFP due to the increased TPR.


    Issue 3
    So what/why is Guyton talking about folks, when he says:

    1)Arteriolar constriction causes a parallel shift upward [like in a transfusion]


    -This is incorrect

    2)The veins simultaneously dilate when a segment of the arterioles constrict

    -It might have something to do with the drug---anybody else wanna take a shot at this?

    3)What does he mean when he says "if any single segment of the circulation constricts". What is "a segment"?

    -I think what he meant was that instead of the entire collection of arteries and arterioles constriction, only a select few do---maybe.

    4)increased vasomotor tone [increased TPR] causes a parallel shift upward on the vascular function curve----YEAH THIS IS TOTALLY WRONG

    -I agree with you. It should be increased venomotor tone causes a parallel shift upward on the vascular function curve. But increased vasomotor tone WILL cause increased TPR--which will move the vascular function curve in a counter-clockwise fashion about that unchanged MSFP.

    All I know is that only two things cause a parallel shift upward on the vascular function curve and they are as follows--according to recent texts:

    1)Increased venous tone [decreased venous compliance]
    -That is correct
    2)Rapid transfusion of blood
    -That is correct

    Does it have something to do with the sympathomimetic drug? Or, has Guyton been correct all these years and current physiology professors/authors have simply been misinterpreting him, thus presenting us with false information in books and in the classroom?
    It was not well understood yet is probably the best answer.

    My 2 cents

    WY
     
  12. the big wand

    the big wand Senior Member
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    This will be true if you assume the arteriole is in its relaxed state initially. Vasomotor tone relates to wall stress, while resistance relates to radius of a vessel. According to Laplace Law, increased radius (vasodilation) will increase wall stress. :)

    Maybe true, if you're talking about the phenomenon "Shunting." If one drug preferentially constricts a renal artery but not others, then blood is shunted/re-directed to other arteries/organs. The physical bulk flow may stretch/dilate those other arteries. But...again, there may be some counteracting mechanisms such as myogenic tone, autoregulation, etc to prevent over-dilating of a vessel in response to increased flow.
     
  13. Bickle

    Bickle future NYC taxi driver
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    Sorry, but I define myself as more than just a student. I'm a complete person, who cant be defined under one category, unlike yourself it seems.
     
  14. rsweeney

    rsweeney Senior Member
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    Sorry, but I define myself as more than just a student. I'm a complete person, who cant be defined under one category, unlike yourself it seems.

    WOW :eek:--Yup, I was specifically referring to dentaldream--get over yourself. Also, get off the substanceless scrutiny bandwagon! Did I ever define you at all? Did I even define define myself? I apologize if you read into that one :rolleyes: Your post reminds me of a humanites class I took a while back!
     
  15. Bickle

    Bickle future NYC taxi driver
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    Well, the way you wrote it, it kind of seemed that who ever didnt really care about your physio brain teasers aren't "authentic students". I think I'm a good student, but I dont spend my days obsessing over minute details of physio textbooks. I guess I'm not an authentic student. I'm much more. :laugh:

    BTW, thanks for the bad karma! :thumbup: :laugh:










    ps if i'm on any bandwagon right now, its the Calgary Flames bandwagon!! Go flames go! :D
     
  16. rsweeney

    rsweeney Senior Member
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    Well, the way you wrote it, it kind of seemed that who ever didnt really care about your physio brain teasers aren't "authentic students".

    Nope, it was not intended that way. I am sorry for the mix-up. You have to understand that it gets very frustrating when you spend a lot of time and effort putting together a post, to then have most people react in disdain. What's sad it that I already knew people would react in disdain. But, no, my statement was not a generalized one. I was addressing those who judged me. It just amazes me how one would take the time to toss around substanceless negative judgments--talk about character and tact. In other words, they were not acting in a professional manner in a professional forum.
     
  17. PERFECT3435

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    excellent posts rsweeney!
     
  18. the big wand

    the big wand Senior Member
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    Just recall a situation where this might happen. During exercise, you want your blood delivered to skeletal muscle instead of the gut. Arteries to the gut constrict and thus shunt blood toward the vasculature of skeletal muscle. The scenario is reversed after eating a meal. :idea:
     

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